Auto merge of #24473 - mmatyas:webgl_fns_buffer, r=jdm

Implement the basic WebGL2 buffer data operations

Adds support for the WebGL2 calls `bufferData`, `bufferSubData`, `copyBufferSubData` and `getBufferSubData`.

Reference: https://www.khronos.org/registry/webgl/specs/latest/2.0/#3.7.3

---

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This patch depends on https://github.com/servo/sparkle/pull/8. Some tests cause a crash for me at the moment, as they depend on other, not yet implemented buffer calls and transform feedback objects.

As for the code, there are a few parts I'm not sure about:

- To get the element byte size of a TypedArray I've wrote a simple `match`, as the relevant field is not published in `rust-mozjs`. Is that okay or there's some other way to get this already?
- The WebGL1 BufferData implementations were copied into the WebGL2 code as a workaround, due to the difference in the available buffer slots (ie. `self.bound_buffer`). An alternative could be is to pass this function and self as parameters to an internal buffer data implementation function, but personally I found that code to be quite ugly.

cc @jdm @zakorgy

---
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- [x] `./mach build -d` does not report any errors (with the sparkle patch)
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #___ (GitHub issue number if applicable)

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- [x] There are tests for these changes OR
- [ ] These changes do not require tests because ___

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1 files changed, 24 insertions, 9 deletions

diff --git a/components/script/dom/webglbuffer.rs b/components/script/dom/webglbuffer.rs
index 9fd8df489d6..182100ae41f 100644
--- a/components/script/dom/webglbuffer.rs
+++ b/components/script/dom/webglbuffer.rs
@@ -3,6 +3,7 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 // https://www.khronos.org/registry/webgl/specs/latest/1.0/webgl.idl
+use crate::dom::bindings::codegen::Bindings::WebGL2RenderingContextBinding::WebGL2RenderingContextConstants;
 use crate::dom::bindings::codegen::Bindings::WebGLBufferBinding;
 use crate::dom::bindings::codegen::Bindings::WebGLRenderingContextBinding::WebGLRenderingContextConstants;
 use crate::dom::bindings::inheritance::Castable;
@@ -16,6 +17,11 @@ use dom_struct::dom_struct;
 use ipc_channel::ipc;
 use std::cell::Cell;
 
+fn target_is_copy_buffer(target: u32) -> bool {
+    target == WebGL2RenderingContextConstants::COPY_READ_BUFFER ||
+        target == WebGL2RenderingContextConstants::COPY_WRITE_BUFFER
+}
+
 #[dom_struct]
 pub struct WebGLBuffer {
     webgl_object: WebGLObject,
@@ -65,7 +71,7 @@ impl WebGLBuffer {
         self.id
     }
 
-    pub fn buffer_data(&self, data: &[u8], usage: u32) -> WebGLResult<()> {
+    pub fn buffer_data(&self, target: u32, data: &[u8], usage: u32) -> WebGLResult<()> {
         match usage {
             WebGLRenderingContextConstants::STREAM_DRAW |
             WebGLRenderingContextConstants::STATIC_DRAW |
@@ -78,11 +84,7 @@ impl WebGLBuffer {
         let (sender, receiver) = ipc::bytes_channel().unwrap();
         self.upcast::<WebGLObject>()
             .context()
-            .send_command(WebGLCommand::BufferData(
-                self.target.get().unwrap(),
-                receiver,
-                usage,
-            ));
+            .send_command(WebGLCommand::BufferData(target, receiver, usage));
         sender.send(data).unwrap();
         Ok(())
     }
@@ -124,11 +126,24 @@ impl WebGLBuffer {
         self.target.get()
     }
 
-    pub fn set_target(&self, target: u32) -> WebGLResult<()> {
-        if self.target.get().map_or(false, |t| t != target) {
+    fn can_bind_to(&self, new_target: u32) -> bool {
+        if let Some(current_target) = self.target.get() {
+            if [current_target, new_target]
+                .contains(&WebGLRenderingContextConstants::ELEMENT_ARRAY_BUFFER)
+            {
+                return target_is_copy_buffer(new_target) || new_target == current_target;
+            }
+        }
+        true
+    }
+
+    pub fn set_target_maybe(&self, target: u32) -> WebGLResult<()> {
+        if !self.can_bind_to(target) {
             return Err(WebGLError::InvalidOperation);
         }
-        self.target.set(Some(target));
+        if !target_is_copy_buffer(target) {
+            self.target.set(Some(target));
+        }
         Ok(())
     }